The invention concerns a process for producing medical electrodes, in particular neutral electrodes, wherein a laminate in web form comprising a non-conductive intermediate carrier and a conductor layer is coated on the side of the conductor layer with an electrically conductive adhesive gel and the laminate-gel combination is shaped to a contour, preferably stamped out, before it is fixed on a carrier on the side remote from the gel. The invention further concerns such a medical electrode.
Medical electrodes are stuck to the skin of a patient for the most widely varying purposes, in order to pick up electrical signals or to introduce and carry away currents (defibrillation neutral electrodes). Particularly in the case of medical bioelectrodes which are used as neutral electrodes in order to carry away currents, it is important that skin contact takes place as uniformly as possible in order to avoid local high current densities. Multi-layer neutral electrodes are already known, which have a carrier for example of foam material on the side which faces away from the skin. The next layer is a laminate comprising an intermediate carrier with a conductor layer, for example aluminum. That conductor layer is then covered on the skin side with an electrically conductive, adhesive gel (for example a skin-friendly hydrogel). In that respect care is to be taken to ensure that the metal conductor layer does not come into direct contact with the skin of the patient.
It is known for the edge of the conductor layer to be covered with gel or an additional insulating element. That structure however is costly and complicated.
In order to shape a covering insulating element, it is necessary to use material of approximately the same surface area as that of the entire electrode, in which case the predominant proportion is cuttings and thus waste.
If the conductor surface is overlappingly covered with gel, that is done using one of two known processes. On the one hand, a flat web of gel can be produced, stamped out in the shape required for the overlapping, and fixed by adhesive precisely over the conductor surface. That process is highly expensive in terms of the material used as additional cover webs have to be employed in the course of the process and it makes high demands in terms of manipulation of the adhesive gel surface.
On the other hand, a liquid pre-mix for the gel can be poured into a reservoir which is provided for that purpose and which is formed by the carrier of the electrode together with the conducting surface (or a cover) and a peripherally extending edge element. That pre-mix then polymerizes, for example with a supply of energy, to form an adhesive hydrogel. In this case also, a considerable amount of waste is produced, for forming the peripherally extending edge element, and handling of the liquid pre-mix is extremely demanding and liable to error. Because of this, such processes are only used by a few manufacturers (possibly only just, one).
The object of the invention is to provide a process with which it is possible to produce a medical electrode in an automated manufacturing procedure, which involves a uniform and reliable transmission of current between the skin of the patient and the electrode.
A further object of the invention is to provide such an electrode.
The process according to the invention is characterised in that the conductor layer is already applied in manufacture of the laminate to the intermediate carrier in web formxe2x80x94preferably by preceding stamping-out-in the form of fields which do not cover the entire intermediate carrier in web form, and that the operation of shaping the laminate-gel combination to contourxe2x80x94which is preferably effected by stamping outxe2x80x94is effected in such a way that the gel laterally projects at least in a region-wise manner with respect to the outer edges of the conductor layer fields which are pre-formed in the laminate.
The basic idea of the process of the invention is firstly that manufacture of the electrode does not as usual involve using a laminate in web form, with simply laminating onto a non-conductive intermediate carrier in web form a conductor layer in web form of the same size, but rather providing upon manufacture a special laminate in which substantially discrete individual fields or areas are arranged on the non-conductive intermediate layer. In that way, after the conductive gel has been applied in a further stamping process, it is possible to implement a stamping operation which involves substantially at all sides a lateral spacing in relation to the electrically conductive individual fields. In contrast to the state of the art in which the gel together with the conductor layer was jointly stamped, the process according to the invention now provides that the gel laterally covers over the outer edges of the conductor layer fields which are pre-formed in the laminate. In that way it is possible to manufacture an electrode in which the conductive adhesive gel layer completely overlaps the conductive (metal) foil wherever contact with the body occurs. That therefore avoids high local current strengths by direct contact of the conductor with the skin, which for example can result in burns. It will be appreciated that the tabs required for connection to the electrode cable can also be caused to project freely without a gel covering in the electrodes according to the invention.
The proposed process is much simpler in procedure than the state of the art as gel coating over the full area involved can be effected. It makes much greater savings in terms of material as no additional materials whatsoever have to be used (the intermediate carrier is used as standard for aluminum laminates (to save on aluminum, to resist creasing and crushing, to afford better tensile strength)).
The electrode according to the invention is therefore characterised in that the gel also laterally surrounds at least in a region-wise manner the outer edges of the conductor layer and extends there to the intermediate carrier.